J. Anim. Sci. 2003. 81:423-431
© 2003 American Society of Animal Science
Dietary fat has minimal effects on fatty acid metabolism transcript concentrations in pigs1
S.-T. Ding*,
,
A. Lapillonne*,
W. C. Heird* and
H. J. Mersmann*,2
* USDA, ARS, Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030-2600, and
and
Department of Animal Science,National Taiwan University, Taipei, Taiwan
2 Correspondence:
1100 Bates St. (phone: 713-798-7128; fax: 713-798-7130; E-mail:
mersmann{at}bcm.tmc.edu).
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Abstract
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Young, crossbred pigs were fed either a low-fat, corn-based diet; a high-fat, tallow-based diet with a considerable saturated fatty acid (FA) content; or a high-fat, fish oil-based diet with a considerable polyunsaturated FA content, for 14 d. There were six pigs per dietary group (approximately 4-wk-old with a body weight of 6.16 kg). The plasma and adipose tissue FA composition reflected the composition of the diet to a large extent, but also reflected de novo FA synthesis coupled with chain elongation and desaturation. The liver and skeletal muscle FA composition reflected the diet and endogenous synthesis, but the indications for preferential incorporation or exclusion of specific FA were greater in these tissues than in plasma or adipose tissue. An important transcription factor for adipocyte differentiation and other aspects of lipid metabolism is adipocyte determination and differentiation-dependent factor 1 (ADD1). Liver ADD1 messenger RNA (mRNA) tended to be decreased (P = 0.06) in the fish oil-fed group, as well as in the combined high-fat-fed groups (tallow + fish oil) compared to the low-fat-fed group (P = 0.06). The muscle acyl-CoA oxidase mRNA tended to be increased in the tallow-fed group and decreased in fish oil-fed groups (P = 0.06). The muscle carnitine palmitoyltransferase mRNA tended to be elevated in both fat-fed groups (P = 0.07). None of the adipose tissue mRNA were changed by the diet (P > 0.20). The observations suggest there are major differences between rodents and pigs in modulation of transcripts associated with lipid metabolism by the dietary FA composition or concentration. Also, in porcine adipose tissue, as well as in liver and skeletal muscle, these transcripts are rather refractory to modification by dietary FA.
Key Words: Acyl-CoA Oxidase • Adipocytes • Carnitine Palmitoyltransferase • Dietary Fat • Fatty Acid Synthase • Messenger Ribonucleic Acid
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Introduction
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Individual long-chain fatty acids (FA) stimulate differentiation of clonal preadipocytes and increase the transcript concentrations for genes associated with differentiation (Amri et al., 1991; Distel et al., 1992). A key transcription factor in preadipocyte differentiation is peroxisome proliferator-activated receptor 
(PPAR). The PPAR functions as a heterodimer with retinoid x receptor 
(RXR), and the heterodimer, PPAR-RXR, must be activated by an appropriate ligand (Rosen et al., 2000; Poisson and Narce, 2001). The FA are potential ligands for PPAR (Tontonoz et al., 1994; Kliewer et al., 1997).
The transcription factor, adipocyte determination and differentiation-dependent factor 1 (ADD1), regulates transcription of fatty acid synthase (FAS) and plays a role in adipocyte differentiation (Kim and Spiegelman, 1996; Kim et al., 1998), perhaps by providing FA or FA-derived ligands for PPAR. Dietary n-3 PUFA reduce hepatic FAS through a reduction of ADD1 expression in rodents (Xu et al., 2001). The ADD1 messenger RNA (mRNA) is highly expressed in porcine adipose tissue (Ding et al., 1999; 2000). Incubation of porcine preadipocytes (i.e., stromal-vascular cells) with C22:6 decreased the ADD1 mRNA and protein concentrations (S.-T. Ding and H. J. Mersmann, unpublished data). In this case, the C22:6 may suppress expression of ADD1, which in turn may decrease FA biosynthesis. Thus, the FA or FA-derived ligand for PPAR may be limited with a consequent decrease in adipocyte differentiation and hypertrophy. To test this hypothesis in vivo, we fed pigs either a high-fat fish oil diet, with a relatively high concentration of C22:6, a high-fat tallow diet with a high concentration of saturated and monounsaturated FA, or a low-fat diet. Transcripts for ADD1 and for other genes associated with FA metabolism were measured in adipose tissue, liver, and skeletal muscle.
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Methods
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Animals and Diets
Eighteen castrated male crossbred pigs (approximately 4 wk of age) were obtained from the Texas Department of Criminal Justice in Huntsville. They weighed 6.16 kg (SD = 1.01) on arrival at the Children’s Nutrition Research Center, where they were placed in individual cages and fed the basal diet (Table 1
). After 1 wk to adapt to their surroundings, cages, and diet, the pigs were divided into three groups, which were fed one of three diets. Each diet consisted of 85 parts basal diet plus one of the following supplemental variations: 15 parts cellulose (low-fat diet; cellulose was Alphacel from ICN Biomedical Research Products, Costa Mesa, CA); 15 parts tallow (high-saturated fat diet; tallow from Dyets Inc. Bethlehem, PA); or 15 parts fish oil (high-polyunsaturated fat diet; menhaden oil from Dyets Inc.). Cholesterol (ICN Biomedical Research Products) was added to the fish oil and low-fat diets to the level reported for tallow; assuming tallow contains 1.09 g of cholesterol/kg and fish oil approximately half this amount, the low-fat diet was supplemented with 164 mg cholesterol/kg diet and the fish oil diet with 82 mg of cholesterol/kg diet. The calculated protein in the experimental diets was 20.4%; the calculated fat was 2.53% for the low-fat diet, and 17.53% for the high-fat tallow and high-fat fish oil diets. The FA composition of the diets is indicated in Table 2. Beginning 3 d before administration of the experimental diets, pigs were fed two meals per day, one at 0800 and the other at 1600. The pigs were fed to approximate ad libitum feeding; feed remaining at 0800 the next day was weighed back, and the amount fed was increased on an individual animal basis when feeders were empty at 0800. Excess feed was kept to a minimum to decrease wasting.
One-half of the pigs from each dietary group was selected at random and killed after being fed the experimental diets for 14 d; pigs were killed beginning at 1000, after the 0800 feeding. The other half of the pigs was killed at 1000 on d 15 of being fed the experimental diets. Pigs were killed with a captive bolt gun coupled with exsanguination. Tissue samples were rapidly removed, wrapped in foil, and frozen in liquid nitrogen to be stored at -70°C. An adipose tissue sample containing the upper and middle layers was removed from the dorsal subcutaneous depot in the neck region, a skeletal muscle sample was removed from the longissimus muscle between the 10th and last ribs, and a liver sample was removed from the right lobe. A blood sample was obtained from the cut anterior vena cava using EDTA as anticoagulant; plasma and diet samples were frozen at -70°C until analysis. The Baylor College of Medicine Institutional Animal Care and Use Committee approved the animal protocol.
Fatty Acid Analysis
Fatty acid analysis was performed as previously described (Lapillonne et al., 2002). Briefly, 1 g of tissue was homogenized with 5 mL of PBS containing 40 mM EDTA, pH 7.4 (Polytron PT-10, Brinkmann Instruments, Westbury, NY). One gram of diet was homogenized into 10 mL of distilled water. Total lipids were extracted from 1 mL of tissue homogenate, 0.4 mL of plasma, or 0.1 mL of diet homogenate using a modification of the methods of Folch et al. (1957) and Bligh and Dyer (1959).
Fatty acid methyl esters were then prepared (Morrison and Smith, 1964). The FA methyl esters were separated by gas chromatography on a 30 m x 0.25 mm i.d., 0.25-Fm film, DB-225 capillary column (J & W Scientific, Folsom, CA) with a Hewlett-Packard 5890 gas chromatograph equipped with a hydrogen flame-ionization detector. Individual FA were identified by comparison to the retention times of standards (Nu Check Prep, Inc., Elysian, MN). The molar proportion of FA was calculated from the chromatograms using a proportional comparison of FA peak areas after each was normalized against the FA molecular mass and flame-ionization response factor. The chromatographic analysis was in duplicate and the data were averaged. Only FA present at 
1.0% are indicated in the Tables.
RNA Analysis
Total RNA was extracted from the powdered, frozen tissues, separated by electrophoresis, blotted to membranes, and hybridized with radiolabeled riboprobes, as previously described (Ding et al., 1999; McNeel et al., 2000b). The RNA probes were synthesized with the Strip-EZ T7 kit (Ambion, Austin, TX). The porcine 18S, acyl-CoA oxidase (ACO), ADD1, FAS, and adipocyte fatty acid-binding protein (aP2) probes were previously described (Ding et al., 1999; 2000); the probes are listed in Table 2
. The FAS probe was derived from a clone provided by S. Clarke at the University of Texas (Mildner and Clarke, 1991). The carnitine palmitoyltransferase I (CPTI) probe was a rat probe (Esser et al., 1996) provided by V. Esser, University of Texas, Dallas. Hybridization was quantified by phosphor-image analysis, as previously described (Ding et al., 2000; McNeel et al., 2000b). The densitometric value for an individual transcript in a sample lane was normalized to the densitometric value for the 18S ribosomal RNA in the same lane.
Statistical Analyses
Fatty acid analysis, growth, and transcript data were analyzed by one-way ANOVA. There were six animals per diet group. Three animals per diet group were randomly selected and killed on each of two consecutive days. Because of the balanced design and close proximity of slaughter days, slaughter day was not considered in the statistical analysis. The means were separated using a Tukey post hoc test.
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Results
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Animal Growth
Pigs in all feeding groups gained the same amount of BW over the 2-wk period—7 kg on average (Table 3). The amount of feed consumed was the same, although the consumption was numerically lower in the two high-dietary-fat groups, as was expected if the pigs were eating to constant energy intake. The feed intake probably would have been significantly lower in the two high-dietary-fat groups compared with the low-fat group with a longer feeding period. The efficiency of gain (gain:feed) was not different between the groups. The calculated DE for the low-fat diet was 3,034 kcal/kg, whereas the DE for the high-fat diets was 4,384 kcal/kg. The calculated gain/DE consumed was 0.258 (kg gain/Mcal of DE ingested) for the low-fat-fed pigs, 0.200 for the tallow-fed pigs, and 0.183 for the fish oil-fed pigs.
Although newborn pigs have little subcutaneous fat and small adipocytes, adipose tissue deposition and adipocyte hypertrophy occur rapidly during the neonatal and growing period. Fat deposition or adipocyte size was not measured in the current studies. However, previous studies indicate major increases in these variables in pigs of comparable ages (e.g., between 32 and 45 d of age, the adipocyte diameters increased from 45 to 53 µm—approximately 48,000 to 78,000 µm3—and the tissue triacylglycerol increased from 502 to 544 mg/g tissue; Steffen et al., 1979).
Diets
The low-fat diet contained <3% fat, with much of the fat contributed by corn (Table 1). Thus, as expected, this diet had a relatively high proportion of palmitic acid (C16:0) and oleic acid (C18:1), a relatively low proportion of stearic acid (C18:0), and a high proportion of linoleic acid (C18:2), the major FA in corn oil (Table 4). The high-fat (17+%), tallow-supplemented diet contained high proportions of the saturated FA, C16:0 and C18:0, as well as the monounsaturated FA, C18:1, coupled with low proportions of C18:2 and other PUFA. The high-fat (17+%), fish oil-supplemented diet contained high proportions of myristic acid (C14:0), C16:0, palmitoleic acid (C16:1), and several PUFA, including eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6); the proportions of C18:0, C18:1, and C18:2 were relatively low. Fatty acids not reported in the diet (<1% of the total), but accumulated in a tissue, probably represent biosynthesis by chain shortening, elongation, and desaturation in that tissue, biosynthesis in another tissue with transport into and accumulation in the analyzed tissue, or vigorous uptake and accumulation of a minor component of the diet.
Plasma Fatty Acid Composition
To a large extent, the distribution of FA in the plasma reflected the distribution in the diet (Table 5). Plasma FA also reflected the de novo synthesis of FA with the primary product being C16:0, which can be extended by the addition of two-carbon units and desaturated. Finally, plasma FA reflected the preferential incorporation of specific FA into individual types of complex lipids. In the low-fat-fed pigs, the proportion of plasma C18:2 was high, reflecting the corn in the diet. The proportion of arachidonic acid (C20:4) was also high, probably reflecting chain elongation and desaturation of C18:2. The C18:1 proportion was low relative to the diet. In tallow-fed pigs, there was a relatively high proportion of C16:0, C18:0, and C18:1, reflecting the diet, but the C18:0 and perhaps C18:1 were low compared to the diet, whereas C18:2 and C20:4 were elevated compared to the diet, suggesting preferential incorporation of specific FA into the plasma FA pool. Feeding of fish oil caused an increase in plasma C20:5, C22:6, and C16:1, and a decrease in C18:1 and C18:2, reflecting composition of the diet. The FA composition of plasma from fish oil-fed pigs was quite different from the FA composition of plasma from low-fat- and tallow-fed pigs.
Adipose Tissue Fatty Acid Composition
The adipose tissue FA composition was generally similar to the diet (Table 6). Adipose tissue from the low-fat-fed pigs had a large percentage of saturated FA (greater C16:0 and C18:0) and monounsaturated FA (C16:1 and C18:1). These FA were probably derived from the diet and from de novo synthesis because with the low-fat diet, there would be considerable de novo FA synthesis in the adipocyte (Allee et al., 1972) to produce C16:0 followed by chain-elongation and desaturation. The proportion of C18:2 in adipose tissue was low compared to the diet (i.e., the proportion of C18:2 was high in the diet, but the total dietary fat concentration was low). In tallow-fed pigs, the proportion of C18:0 in adipose tissue was lower than in the diet, perhaps indicating lower absorption from the gut or discrimination against C18:0 incorporation into adipocyte triacylglycerol, the predominant lipid in adipocytes. The proportions of monounsaturated FA (C16:1 and C18:1) were greater than in the diet suggesting desaturase activity. Fish oil-fed pigs had lower C14:0, but greater C18:0 and C18:1 in adipose tissue than in the diet, perhaps reflecting elongation and desaturation of dietary FA. The very long-chain PUFA (C20:5, C22:5, and C22:6) were all elevated in adipose tissue from fish oil-fed pigs compared to adipose tissue from pigs fed the other two diets. However, the proportions of these PUFA were lower than those in the diet, reflecting tissue specificity for incorporation of FA into adipocyte complex lipids (primarily triacylglycerol).
Liver Fatty Acid Composition
The liver FA composition reflected the diet FA composition to some extent (Table 7). However, in all three dietary groups, the proportion of C18:0 was very high compared to that in the diet, whereas the proportion of C16:0 was low compared to the diet. Perhaps this reflects elongation of C16:0. The proportions of monounsaturated FA were low in liver, compared to those in the diets. The liver had a greater proportion of PUFA compared to the diets. The low-fat- and high-fat, tallow-fed groups had a very high proportion of C20:4 compared to that in the diet, probably reflecting elongation and desaturation of C18:2. The proportion of C22:5 and C22:6 also was elevated in the liver compared with the diet, perhaps reflecting preferential incorporation of these very long-chain PUFA into liver lipids. Fish oil-fed pigs had lower C18:1, C18:2, and C20:4, and higher n-3 PUFA (C20:5, C22:5, and C22:6) in the liver than the low-fat-fed and tallow-fed pigs. The data indicate that hepatic FA composition reflects the dietary FA composition to a large extent, but there are numerous modifications suggesting FA elongation and desaturation coupled with preferential incorporation of individual FA into or exclusion of individual FA from complex lipids.
Skeletal Muscle Fatty Acid Composition
Compared to the diet, skeletal muscle in the low-fat-fed pigs contained greater proportions of C14:0, C18:0, erucic acid (C22:1), docosadienoic acid (C22:2), C20:4, and adrenic acid (C22:4) with lesser proportions of C18:1 and C18:2 (Table 8). This pattern suggests not only preferential incorporation of specific FA into muscle complex lipids, but also desaturation and elongation in the tissue to produce the distinct patterns. In tallow-fed pigs, the muscle contained greater proportions of C22:1, C22:2, and C20:4, and lesser proportions of C18:0 than in the diet. Feeding fish oil produced greater proportions of muscle C18:0, C18:1, C22:2, and C20:4, with lesser proportions of C14:0 and C16:1 compared with the diet. The proportions of C20:5 and C22:6 in skeletal muscle of fish oil-fed pigs were lower than in the diet, but considerably elevated compared to the low-fat- or tallow-fed pigs.
Transcript Concentrations
The liver ADD1 mRNA concentration tended to be lower (P < 0.10) in the fish oil-fed group compared to the low-fat-fed group (Table 9). The mean ADD1 for the combined two high-fat-fed groups (tallow and fish oil) was 69% and also tended to be lower (P = 0.06) than that for the low-fat-fed group. There was no difference in the ACO or FAS transcript concentrations across feeding groups. In muscle, the ACO mRNA concentration was numerically greater in the tallow-fed group and numerically less in the fish oil-fed group compared to the low-fat-fed group. The ACO mRNA concentration in the fish oil-fed group tended to be lower (P < 0.10) than in the tallow-fed group. The muscle CPTI transcript concentration was numerically greater in the fish oil-fed group and tended to be elevated (P < 0.10) in the tallow-fed group compared to the low-fat-fed group. The mean CPTI for the combined two high-fat-fed groups (tallow and fish oil), 178%, also tended to be greater (P = 0.06) than that for the low-fat-fed group. In adipose tissue, there was no difference in ADD1, ACO, CPTI, FAS, or aP2 transcript concentrations across dietary groups.
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Table 9. Relative transcript concentrations in liver, muscle, and adipose tissue from pigs fed low-fat or high-fat dietsa
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Discussion
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It has been demonstrated repeatedly that the pig incorporates dietary FA into tissue (Sink et al., 1964; Mason and Sewell, 1967; Smith et al., 1996b) and plasma lipids (Smith et al., 1996a). Thus, to a large extent, tissue FA composition reflects the FA composition of the diet. Our observations indicate that after 2 wk of feeding a high-fat diet, there were large changes in plasma and tissue FA composition that reflect the dietary FA composition. In addition to incorporation of dietary FA, there is de novo FA synthesis in porcine adipose tissue, coupled with elongation and desaturation of FA in adipose tissue and in other tissues. Finally, tissue FA composition also reflects the specific incorporation of individual FA into complex lipids, as dictated by the selectivity of the enzymes synthesizing the various phospholipids, cholesterol esters, and diacylglycerols and triacylglycerols (Lands et al., 1990).
In rodent liver, ADD1 and FAS expression is inhibited by dietary safflower oil and fish oil, which contain large amounts of PUFA (Xu et al., 1999; Yahagi et al., 1999). The PUFA inhibit expression of ADD1 by increasing the mRNA degradation rate, and not by decreasing the transcription rate of the gene (Xu et al., 2001). This results in a decrease in ADD1 mRNA that in turn reduces the transcription rate of FAS in rodent hepatocytes.
The ADD1 mRNA is expressed to a considerable extent in porcine adipose tissue compared to several other tissues (Ding et al., 1999; 2000). In chickens, pigs, and rabbits, the extent of expression of ADD1 in liver compared to adipose tissue depends on the extent to which each tissue synthesizes FA (Gondret et al., 2001). For example, in chickens, in which de novo FA synthesis dominates in the liver, the liver ADD1 and FAS mRNA are expressed to a greater extent than in adipose tissue. In the pig, where de novo FA synthesis dominates in the adipose tissue (O’Hea and Leveille, 1969), the adipose tissue ADD1 and FAS mRNA are expressed to a greater extent than in liver. In the rabbit, where FA synthesis occurs in both adipose tissue and liver, the ADD1 and FAS mRNA are equally expressed in both tissues. Because we observed a considerable decrease in both the ADD1 mRNA and protein in differentiating porcine preadipocytes acutely treated with C22:6 (S.-T. Ding and H. J. Mersmann, unpublished data), we expected that there would be a decrease in adipose tissue ADD1 in vivo in pigs fed fish oil, with an elevated concentration of C22:6. However, although C22:6 was incorporated into all the tissues from fish oil-fed pigs, including adipose tissue, only the liver ADD1 mRNA tended to be decreased (Table 9). Perhaps the greater effect in liver compared to adipose tissue relates to the much higher percentage of n-3 PUFA accumulation in the liver than in adipose tissue (Tables 6 and 7).
The observation of altered transcript concentrations in cells treated with specific FA in vitro and in tissues isolated from animals fed specific high-fat diets may depend on the timing of the transcript measurements. Thus, in porcine preadipocytes differentiating in vitro in the presence of C18:1, transcripts associated with differentiation are increased at 1 and 5 d, but at 10 d of treatment, the transcript concentrations are not different from the control levels (Ding and Mersmann, 2001). Modification of adipose tissue transcripts by dietary lipids has been demonstrated after various periods of feeding the experimental diets. In rats fed a high-fat vs low-fat diet for 8 d, the PPAR and aP2 mRNA concentrations are decreased, whereas in rats fed a high-fat vs low-fat diet for 30 d, the transcripts are increased (Margareto et al., 2001). In rats fed fish oil for 4 wk, the adipose tissue FAS, LPL, CCPPT enhancer binder protein alpha (C/EBP), etc., transcript concentrations are decreased (Raclot et al., 1997). Pigs fed high-fat diets for 12 wk have increased adipose tissue PPAR mRNA concentrations (Spurlock et al., 2000). Although our data indicate porcine adipocyte ADD1 mRNA and protein concentrations are decreased after treatment with C22:6 in vitro, we did not observe a comparable decrease in adipose tissue ADD1 mRNA concentration in vivo after feeding fish oil for 2 wk. Perhaps the lack of response in vivo (Table 9) represents species differences. Certainly the fish oil FA concentrations were elevated in the adipose tissue (Table 6). However, the timing of the RNA measurements (i.e., 2 wk) may not have been appropriate.
The ACO enzyme is the initiating enzyme for peroxisomal FA ß-oxidation, whereas CPTI is the rate-limiting enzyme for mitochondrial FA ß-oxidation. The expression of the genes for ACO and CPTI is regulated by PPAR (Bell et al., 1998; Desvergne and Wahli, 1999). The ACO is expressed in several porcine tissues with the liver and adipose tissue mRNA concentrations higher than in skeletal muscle (Ding et al., 2000). The PUFA are candidate ligands for PPAR, so that activation of PPAR by a PUFA could increase the expression of ACO and CPTI. Given the individual tissue access to the various FA, evidenced by the changes in FA composition (Tables 5 to 8), it is surprising that substantial changes in the transcript concentrations for ACO were not observed. The trend in muscle resulted from a difference between tallow- and fish oil-fed pigs (Table 9), suggesting that ingestion of fish oil lowered the ACO mRNA concentration. This is in contrast to rats fed fish oil, wherein the ACO mRNA concentration in liver was elevated (not changed in pig liver; Table 9) and was not changed in muscle (Neschen et al., 2002). The CPTI tended to be elevated in the muscle of the tallow-fed pigs and was numerically increased in the fish oil-fed pigs compared with the low-fat-fed pigs, suggesting that high fat feeding increased porcine muscle CPTI. In adipose tissue, CPTI expression was not affected by dietary FA composition or fat content.
After 5 wk of feeding pigs high-fat diets containing a predominant individual FA compared with a low-fat diet, glucose incorporation into adipose tissue lipids was inhibited (Smith et al., 1996b). The most effective FA is C16:0 followed by C14:1/C16:1, and then by C18:0, C18:1, or C18:2. These data indicate that porcine adipose tissue lipogenesis is inhibited by individual FA and amplifies earlier data indicating decreased lipogenesis in adipose tissue from high-fat-fed pigs (Allee et al., 1972). Because this biosynthetic pathway is depressed by fat feeding, one might surmise that at least a portion of the regulation probably resulted from decreased transcription of mRNA for genes associated with lipid synthesis (not measured). It should be noted that porcine adipose tissue is rather refractory to regulation of transcripts by energy intake with a decrease in transcript concentration only evident after pigs were fasted for several days, but not when intake was severely restricted for weeks (Spurlock et al., 1998; McNeel et al., 2000a; McNeel and Mersmann, 2000). We also observed that the ß-adrenergic receptors in porcine adipose tissue are refractory to dietary fat concentration and composition; receptor number is similar in low- and high-fat-fed pigs, regardless of whether the high-fat diet is saturated or unsaturated (Mersmann et al., 1992; 1995). The fact that transcripts associated with porcine adipose tissue lipogenesis (FAS and aP2) were refractory to dietary fat concentration and composition in the present study (Table 9) must be cautiously interpreted because of the results of Smith et al. (1996b), discussed above, and because there was only one time point—14 d. Many transcripts have transient changes in response to a stimulus, so that the time selected for sampling may not be appropriate for individual transcripts expressed in specific tissues.
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Implications
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As demonstrated many times, the fatty acid composition of the diet is reflected to a large extent in the fatty acid composition of pigs. Feeding an altered fatty acid diet for as little as 2 wk was long enough to cause extensive change in the tissue fatty acid composition. The messenger ribonucleic acid for genes associated with multiple aspects of lipid metabolism were not greatly modified, suggesting that some porcine genes are refractory to regulation by dietary fatty acids.
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Footnotes
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1 We thank J. Cunningham, F. Biggs, and J. Stubblefield for care and feeding of animals, B. Hunter-Sexton for secretarial assistance, and L. Loddeke for editorial guidance. This work is a publication of the USDA, ARS, Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas. This project has been funded in part with federal funds from the USDA, ARS under Cooperative Agreement No. 58-6250-6001. The contents of this publication do not necessarily reflect the views or policies of the USDA, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. government. A. Lapillone was funded in part by the Association Nutrition, Santé et Charcuteries, France. 
Received for publication May 22, 2002.
Accepted for publication October 24, 2002.
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Abstract
Introduction
